Collapse Theories

Theories Purport to Explain the Unexplainable

All theories to be taken seriously
must explain the collapses of the Twin Towers
as the result of some chain of events triggered by the
jet collisions.
To this end a variety of "theories" have been advanced.
They range from vague notions of forces too immense to imagine,
to partial explanations with huge gaps filled in by hand-waving,
but are nevertheless
dignified by publication.

Core meltdown
is more a notion than a theory.
It is invoked through comparing the heat of the building fires
to that of nuclear power plants,
and supposes that the fires
melted the structural steel.
This theory can be used in conjunction with a pancake theory,
but usually the idea of core meltdown is so compelling by itself
that the pancake scenario isn't required.
Since the core meltdown theory isn't endorsed by any official
government report, it is frequently used in straw-man attacks
against challenges to the official story, as in articles in
Scientific American and
Popular Mechanics.

The progressive collapse theory
is the root of all the official building collapse theories.
The mass of the overhanging part of the building
simply crushes the part underneath, accelerating as it falls.
The two major variants of the progressive collapse theory are
the truss failure theory,
endorsed by FEMA,
and the
column failure theory,
endorsed by NIST.

The column failure theory
holds that the fires weakened the columns on at least one floor sufficiently
to cause the columns to buckle, and the upper section of the building
to come falling down.
To explain how all the columns on one level could suddenly collapse,
column failure theories sometimes feature
collapse initiation theories.

The creep buckling theory explains how the weakening
of some columns due to heat could cause them to buckle,
starting the spread of a kind of buckle contagion
through the remaining columns.

The progressing column instability theory
is apparently very similar to the creep buckling theory,
but allows the columns to spread failure contagion without buckling.
This theory is a key ingredient in
NIST's Global Analysis.

Once the columns fail in unison, it is still necessary
to crush the rest of the tower from top to bottom.

The pile-driver theory
supposes that the top
of each tower acted like a giant battering ram, crushing the
intact portion of the tower from top to bottom.

The truss failure theory
blames trusses under the floors, which are more easily heated than columns,
and/or their connections to the columns.
The failure of the floor trusses precipitates a chain reaction
of floors falling on one another,
which in turn leads to total building collapse.
The truss failure theory is better known as the pancake theory.
To explain how a whole floor could fall, despite uneven fire stress,
requires a truss failure contagion theory.

The zipper theory
explains how all of the trusses on a floor could fall in rapid succession
because of a domino-effect failure of their column connections.
The zipper theory is much easier to understand if one erases,
as did NOVA,
the perpendicular cross-trusses and floor pans,
and imagines the floor as a series of parallel trusses resting on weak
angle brackets.

Once the first floor falls on the second, it must somehow exceed the
design loads of the one below, which should have been able to
easily absorb the impact of the first floor falling about nine feet,
especially if it didn't fall all at once.
Theories that explain this generally blame some aspect of building
design and/or materials.

The angle bracket theory
helps to explain the cascade of floor collapses below the fire zone
by suggesting that engineers forgot to apply
standard engineering practices
when designing the column connections of the floor trusses.
Mis-describing
the welded steel shelves that supported the truss ends as
angle brackets helps us imagine this.

Once the floor diaphragms have started to pancake down
between the core and outer wall,
it is still necessary to dispose of the dense steel grid constituting the
outer wall,
and the steel lattice of the
core structure.
This requires some form of sudden column failure theory.
Such theories are usually only implied in tellings
of the truss failure theory.
Sections of the outer wall and core structure are supposed to
immediately collapse from lack of lateral support
once the floor diaphragms fall away.
Since the perimeter wall and core structure were easily self-supporting
except possibly in high winds, sudden column failure theories
usually take some liberties in describing the architecture of the
perimeter wall and core structures.

The column splice failure theory has the outer wall
breaking up along column splice connections between
the three-story-high by three-column-wide prefabricated sections.
This theory is easier to accept if one forgets that every set
of three column splice connections was surrounded on both sides
by six continuous column spans,
bound to the spliced columns above and below
by horizontal spandrel plates four feet high.

The freestanding core column theory has the core columns
suddenly buckling catastrophically due to lack of lateral support
from the floor diaphragms.
This theory depends at least on the core columns being freestanding,
as the FEMA Report
allows,
in contrast to
construction photos
that show them to be cross-braced
by horizontal beams and diagonal trussing.

The shockwave theory
postulates some unspecified "shockwave" which travels ahead
of the crushing mass, breaking up the building.
Shockwave theories tend to be found in amateur attempts
at accounting for the building collapses.